Schematics from NEC LCD1830 inverter: ALPS UHP061104

lcd inverter schematic

Here is a reverse engineered drawing from an inverter for the background light from a NEC LCD1830 TFT.

Two transistors were broken: Q8 and Q9. Fuse had been blown and R11 thru R14 were badly welded.

I hope it helps someone.

w_m0zart

backlight inverter schematic

I started troubleshooting my NEC LCD 1830 do to the monitor flicker problem. The monitor when turn on will display image for couple of second then turn black. The monitor status led is still green. This will happen each time it is turn on. The symptom at appear to come from the inverter board. I've check it will oscilloscope
and the high voltage circuit is weak and intermittent. Your schematic of the inverter was very helpful in troubleshooting this problem.

Thank you.

lcd inverter schematics

Hello w_m0zart!
Thank you very very much for this schematic.
Symptom: Backlight flashes short after start and then shut down.
I've invested several hours:
power board
- checked out power supply capacitors
- fuse 25V / 2.5A
inverterboard
- replaced C11 and C12 = 180nF / 250V
- check fuse F1

When the monitor was warm > 25° - it works
Next day - dark screen.

replaced the whole inverter board --> the same
Then I found your schematic:
CN1 / 7: 250 Hz square 8Vss = duty cycle for brightness

The protection circuit causes shut down the backlight.

Each lamp connector CN2 – CN5 has a feedback with a rectifier. The DC voltage is measured above C13, C22, C24 and C25 and should be about 5V.
The comparator U1C and U1D compare this voltage against 1.55V (Pin 8,10 – C16).

The feedback of CN5.2 ( C25) had only 1V in cold condition. So the backlight shut down.
Next try only with power OFF / ON.
I change the connector CN5 and CN4 and also CN2 an CN3 – oh, oh – this fault moves to C24.
Okay, the backlight has a little problem. This is okay, because it has plenty of hours on duty every working day the last five years.

Change R28 from 680Ohm to 1kOhm, and increase C16 from 1µF to 220µF

Now the backlight turns on for 10sec. ignoring the protection circuit.
Backlight warm up and turns to normal operation.

Attention: This modification is no general repairing method for the dark backlight.
You’ve carefully checkout the behaviour with an oscilloscope before your change the components. Check the power consumption on the 12V CN1 / 1 (1.2A @brightness=50%; 2.2A @ brightness= 100%).
In case of disabling the protection circuit even for 10 seconds you might destroy the power circuit or the high voltage inverter.
:idea: This case: more or less weakness of the backlight bulb.

Good Luck!
Werner

nec lcd1830

R11 - R14 badly welded. Resoldered and monitor works like new. Thanks!!!!

uhp061104

Oh my I've been looking for info on this inverter board for ages, I've got two of these monitors that both blow fuses. Can I assume that I should

1. replace bulbs and pico fuses - old bulbs set off the over current detection?

2. troubleshoot any remaining problems


And many thanks for sharing your work with us!!

schematic inverter tft

> 1. replace bulbs and pico fuses - old bulbs set off the over current detection?
yes this seems very likely possible.

> 2. troubleshoot any remaining problems

Please, be more precise in what you mean.

alps uhp061104

ahh well at the time I didn't know what problems remained

however I have repaired the unit and the monitor lived happily ever after.

lcd backlight inverter schematic

I suppose I should put in my 2 cents worth here, and share what I've learned.

I had an 1810 display, not an 1830 (the 1810 has *8* lamps and a rather lossy screen with a near 180 degree viewing angle, very nice especially considering how old it is) - but your schematic was still helpful in that the design was similar enough... I had two bad (shorted) transistors on one of the transformer psuedo multivibrator output circuits. on the 1810 they simply drive four series-parallel bulb circuits, they double up the output circuit (two sets of transistors and transformers) and then take one side of the output on each transformer and ground it. The other side, I'll call it the "high" side of the two transformers - is used to drive two bulbs in series.

but the basic circuit, even the drive transistors, are the same types. The protection circuit is similar but there is also a 5th "master" fuse feeding the "big powerdown fet" and smaller fuses at each of the 4 subsections.

I suppose sometime soon I should try to generate a schematic for this board, as I have another 1810(the DVI input version) waiting for the same repair treatment...

if you can release the orcad .sch file that would be a timesaver but either way - I figure there is a lot excellent monitors out there that can be saved from the trashpile (and shame on NEC for leaving the schematic for the inverter boards out of the service manuals!)

lcd monitor inverter schematic

Here is an Orcad formatted file.

It contains several NEC Multisync related (unfinished) schematics from the LCD 1810/1830.

The inverter board HIU-391C (Partially; from the LCD 1810, which I tried to repair, but the scaler IC had severe heating problems. Later on I bought another one. It had the same problem).

The inverter board ALPS UHP061104

Power supply PCB DC-DC Conv. PWB PWE-627

The Control PCB PWE-588

The Control PWB (This is only the PCB with front panel switches)

The PCB with the AD Converter and Scaler E46669-711V

Good luck.

nec lcd 1830

I have an NEC LCD 2010X that is having the same issue, intermittent backlight flickering on and off. This is the second one I have had with this issue. The first one just plain stopped coming on (still had green led). I purchased a second one off of ebay that had good working backlights but cracked LCD screen I used all the guts from the ebay one and just the LCD screen from the flickering one to create a good working monitor. It is now starting to do the same thing. I am hoping that the inverter is close to the same so I can try the repairs listed here. Does anyone have any suggestions??

nec 1830 lcd inverter

thanks. I have a "complete" service manual for the 1810 (but no backlight schematic!!!) and if anyone wants a copy of the pdf, please feel free to send me an email...

dolphin
strangeanimals
net

and I will provide you a set.

inverter board schematic

Thanks for the schematic, really helped making things clear..I wonder though, I blew the 5102 Fet, but I have NO idea about the replacement for it. Does anyone have any clue which device this is?

Thanks!

lcd inverter schema

I am also working on the Nec 1830 model inverter. Q8 and Q9 still left to replace. Has anyone found a suitable replacement for this transistor (FMMT619) ?

backlight inverter circuit

mini-me said:

I am also working on the Nec 1830 model inverter. Q8 and Q9 still left to replace. Has anyone found a suitable replacement for this transistor (FMMT619) ?

Click to expand...

I have used the ZXTN25015DFHTA from Zetex, which seems to be doing very well. It's stocked by digikey.

hiu-391c

hey all, lookin for some tips here,

i have the same nec lcd1830 white monitor, and it has the failing backlight problem,
i turn on the lcd and the backlight goes dead after like 15 seconds, the lcd still works,
i put a white led flashlight up to the screen to verify and screen still works, just no backlight...
now im on a low budget, not alot of money to buy the new inverter board previously mentioned in this post, so im looking for the cheapest and quickest alternative fix,

any help and info would be great from anyone who has fixed this monitor in the past,
i know its not difficult to fix, i just need to know what to fix, as i dont have an oscilliscope or testing tools like that, all i have is a multimeter and a soldering pen, i have plenty of old mobo's and electronics i could pick parts off of, or even better i have a parts supplier 5 blocks away,
just need to know the stuff to pull and replace, or alternatives to replace the dead ones with

like i siad, desperate and low budget, any help is more then no help
thanx all

lcd1830

It sounds like it may be a connection problem. Inspect the inverter board for bad/cold solder connections, especially around the 4 resistors mentioned in an earlier post. use a fine tip soldering iron.

lcd inverter board schematic

some excellent and useful advice posted here - thanks to all who contributed.

I'm currently reverse engineering the HIU-391C pcb and hope to post the schematic shortly.

yec inverter board schematic

Many thanks to w_m0zart !
Great work to reverse engineer the inverter circuit! Without this I had not been able to repair the monitor.

I have got a defect LCD1830 the backlight off. With the schematic and the comments in this forum I find a way to get the backlight working.
At my LCD1830 the comperator shuts down after 175ms operation. Due to all 4 current feedbacks increase the voltage with the same gradient and the comperators reference voltage at pin 8/10 have also the same gradient, I guess the bulb tubs are aged. Changing C16 to about 5uF does not help, but with 220 uF the backlight is switching on.
With 100% brightness the inverter draws 2,7A at cold condition and 2,5 A at warm state.
The current feedback voltage is about 7 V at every of the 4 bulb tubes. (C25, C24, ...)
Are these values similar to these from the others in this forum? The protection circuit does not switch off at static operation, so I think the feedback current is ok.

lcd backlight schematic

Hello,

I also have an NEC lcd 1830.
After flickering of the screen it went black.
Now it stays black but the lite goes on green.
When i push the reset button i see very dark a small display.
i used it for many years and almost the hole day.
Is this the backlight or can it also be something else.
Is it worth repairing or should i look for a new one?

thanks in advance

tft inverter schematic

Thanks for the schematic! Problem found. R11 badly "welded" on one end causing intermittent operation. Seems to be common on these from the other posts I read